In 1950 for the first time, the ankle-brachial index (ABI) was described by Winsor as “ratio of the systolic blood pressure (SBP) measured at the ankle to that measured at the brachial artery”. At the beginning this parameter was employed as a non-invasive method to screen peripheral artery disease (PAD) in lower extremities.
Later, studies showed that even in the absence of symptoms of PAD, the ABI can serve as a prognostic marker for cardiovascular diseases (CVD), hence an indicator of atherosclerosis at other vascular sites.
For the measurement patient should rest supine in a warm room for at least 10 minutes before testing. the average brachial pressure in that arm and ankle pressure in the leg is recorded sequentially using a oscillometric pressure cuff. The index will be calculated according to the formula seen below. An ABI ratio between 1.0 and 1.4 is considered as normal.
ABI= ankle SBP/brachial SBP
Patients suffering from CVD who also have a low ABI show higher mortality rate compared with patients with CVD who have a normal ABI. As one of the most available markers of atherosclerosis, the ABI is a highly appropriate measurement for CVD risk assessment specially in primary care.